Lubricating compositions having utility as engine oil formulations typically contain dispersants, detergents, antiwear agents and anti-foamants as well as other types of lubricants. Lubricating oil compositions of this type typically control sludge and varnish formation and, in general, promote good engine life. No one typical lubricating oil composition necessarily solves all the deleterious effects known to occur with an automotive engine.
A lubricating oil composition that performs adequately in one engine at given operating conditions does not necessarily perform adequately when used in a different engine or under different conditions. While theoretically, lubricants could be designed for each possible combination of engine and service condition, such a strategy would be unpracticable because many different types of engines exist and the engines are used under different conditions. Accordingly, lubricants that perform well in different types of engines and across a broad spectrum of conditions (e.g., fuel type, operating load and temperature) are desired. Design of lubricating oil compositions is further complicated in that the concentrated mixture of chemicals added to lubricating oil base stocks to import desirable properties should perform well over a broad range of different quality base stocks. Meeting these requirements has been extremely difficult because the formulations are complicated, tests to ascertain whether a lubricant performs well are extremely expensive and time consuming, and collecting field test data is difficult since variables cannot be sufficiently controlled.
W/O 95/29976 (Block et al., Exxon Chemical Patents Inc., International Publication Date of Nov. 9, 1995) relates to a lubricating oil having as ashless nitrogenous TBN source together with ash containing detergent having a TBN in excess of 100, a source of magnesium, and metal dihydrocarbyl dithiophosphate with predominantly or exclusively secondary hydrocarbyl groups. This reference relates to a composition comprising a major amount of an oil of lubricating viscosity having a sulfated ash content between 0.35 and 2 mass percent and (A) a nitrogenous TBN source selected from the group consisting of ashless nitrogen containing dispersants, ashless nitrogen containing dispersant viscosity modifiers, oil-soluble aliphatics, oxyalkyl or arylalkyl amines and mixtures thereof; (B) a metal salt of an oil-soluble acid having a TBN in excess of 100; (C) at least 500 ppm (mass) magnesium; and (D) at least one metal dihydrocarbyl dithiophosphate. The nitrogenous source provides at least about 1.5 TBN to the finished lubricant. The metal salt of an oil-soluble acid provides at least about 40% of the total TBN of the composition. At least 50 mole percent of the hydrocarbyl groups of the dithiophosphate are secondary. Overbased magnesium sulfonate may be used as the metal salt of an oil-soluble sulfonic acid having a TBN in excess of 100 and the additive providing at least 500 ppm (mass) magnesium. The lubricant may be free of aromatic amines having at least two aromatic groups attached directly to the nitrogen. It may have at least 100 ppm (mass) boron and at least 1000 ppm (mass) phosphorus. The boron-to-nitrogen ratio is at least 0.1.
U.S. Pat. No. 4,801,390 (Robson, Jan. 31, 1989) relates to lubricating compositions, particularly for crankcase lubrications of gasoline and diesel engines in automobiles and trucks that have improved viscometric properties by the incorporation of an ashless dispersant and a dispersant viscosity improver with increased boron content of at least 0.02 weight percent of the composition, preferably in the form of an ashless dispersant borated to a higher level.
U.S. Pat. No. 3,087,936 (LeSuer, Apr. 30, 1963) and U.S. Pat. No. 3,254,025 (LeSuer, May 31, 1966) relate to oil-soluble nitrogen and boron-containing compositions and to the process of preparing the same. The compositions of this reference are usefull as additives in lubricants, especially lubricants intended for use in internal combustion engines, gears, and power transmitting units.